Double-side polishing (DSP) is described in U.S. Pat. No. 3,691,694, for example.
In accordance with one embodiment of DSP as described in EP 208 315 B1, semiconductor wafers in “carrier plates” composed of metal or plastic, which have suitably dimensioned cut-outs, are moved between two rotating polishing plates covered with a polishing pad in the presence of a polishing sol on a path predetermined by the machine and process parameters, and are thereby polished.
DSP is conventionally carried out using a polishing pad composed of homogeneous, porous polymer foam, as described in DE 100 04 578 C1, for example, where it is also stated that the polishing pad adhering to the upper polishing plate is permeated by a network of channels and the polishing pad adhering to the lower polishing plate has a smooth surface without such a texture. This measure is intended firstly to ensure homogeneous distribution of the polishing agent used during the polishing, and secondly to prevent the semiconductor wafer from sticking to the upper polishing pad when the upper polishing plate is lifted after polishing has been completed.
In addition to DSP, so-called CMP polishing is used in order to eliminate defects and to reduce the surface roughness. In the case of CMP, a softer polishing pad is used than in the case of DSP. Moreover, only one side of the semiconductor wafer is polished by means of CMP, namely the side on which components are subsequently intended to be fabricated. CMP methods are described for example in US 2002-0077039 and in US 2008-0305722.
The German Patent Application DE 102 007 035 266 A1 describes a method for polishing a substrate composed of silicon material, comprising two polishing steps of the FAP type, which differ in that a polishing agent slurry containing non-bonded abrasive substance as a solid is introduced between the substrate and the polishing pad in one polishing step, while in the second polishing step the polishing agent slurry is replaced by a polishing agent solution that is free of solids. FAP denotes fixed abrasive polishing, which describes a polishing method that uses polishing pads containing fixedly bonded abrasives.
Thus, there are polishing methods using polishing pads which contain no abrasives, wherein abrasives in the form of a polishing sol are supplied in this case, and also polishing methods using polishing pads containing abrasives, wherein a polishing sol does not have to be supplied.
All these methods are disadvantageous with regard to the geometry and/or nanotopology of the polished wafers. DSP and CMP lead to a decrease in thickness at the edge (Edge Roll-Off). FAP is disadvantageous with regard to the surface roughness.